A photographic multi-layer film base comprising 1,4-cyclohexane dimethanol

ABSTRACT

This invention relates to a poly(ethylene terephthalate)-based photographic multilayer film base having improved properties with regard to cutting and finishing operations compared to conventional PET film base. A specified amount of monomeric units derived from 1,4-cyclohexanedimethanol (CHDM) is used in at least two layers of the multilayer structure, such that the multilayer film base has a specified cutting-related property.

FIELD OF THE INVENTION

[0001] This invention relates to a photographic polyester multilayerfilm base having improved properties. The multilayer film base comprisesPET-based polyester materials with a specified relationship between thelevel of monomeric units derived from 1,4-cyclohexane dimethanol (CHDM)in a first layer and the level of 1,4-cyclohexane dimethanol in theother layers of the multilayer film base such that a specifiedcutting-related property is obtained.

BACKGROUND OF THE INVENTION

[0002] Silver-halide photographic elements comprise one or morelight-sensitive layers coated on a support. Typically the supportcomprises a sheet of a transparent or translucent film, commonlyreferred to as a film base. Other layers, such as backing or subbinglayers, may be laminated onto either side of the film base. Commonfilm-base materials for photographic elements are cellulose triacetate(CTA) and poly(ethylene terephthalate) (PET). More recently it has beenproposed to use poly(ethylene naphthalate) (PEN) as a film base forphotographic elements which are intended to be used in a cartridge ofreduced diameter which requires rolling the film more tightly thanpreviously.

[0003] CTA has generally a good mix of physical properties for varioustypes of photographic films. However, its manufacturing process involveshigh levels of gaseous emissions, and it is relatively costly. Themanufacturing process for PET, on the other hand, is environmentallybenign. Poly(ethylene terephthalate) (PET) films exhibit excellentproperties for use as photographic film base with regard totransparency, dimensional stability, mechanical strength, resistance tothermal deformation. However, compared to CTA, PET films are extremelytough and, therefore, not well suited for finishing operations, i.e.,slitting, chopping and/or perforating processes, which are required inthe manufacture or preparation of photographic films. Moreover, suchfilms are difficult to cut in various steps of the photofinishingprocess such as splicing, notching, and sleeving. This is one of thereasons that PET materials have been considered unusable as a film basein certain consumer photographic film applications, such as 35 mm film,especially consumer films requiring non-centralized external processingor minilab processing where finishing must be easily handled. PETmaterials are presently used in photographic films in which lessdecentralized processing is not required, for example, X-ray films,motion picture films, and graphic arts films. With respect to the lattertypes of films, adjustments to processing can be more easily made tohandle cutting and the like. The process for making a polyester-basedphotographic film base typically comprises the steps of casting a moltenpolyester resin in a machine direction onto a casting surface to form acontinuous sheet, drafting the sheet by stretching in the machinedirection, tentering the sheet by stretching in the transversedirection, heat-setting the drafted and tentered sheet, and cooling theheat-set sheet to form a stretched, heat-set film, such as described in,e.g., U.S. Pat. No. 4,141,735, the disclosure of which is incorporatedby reference herein. U.S. Pat. Nos. 5,385,704 and 5,607,826 disclose amethod for improving the finishing characteristics of photographicmaterials employing a PET film base involving lowering the planarbirefringence of the film base to below 0.150 by performing adetentering step which allows the tentered film to shrink in width by 2to 20% (pref. 10-18%) after the heat-setting step during filmmanufacturing. Improvement in finishing characteristics of PET-basedphotographic film, as manifested by decrease in dirt and debrisgenerated during finishing operations, is also disclosed in U.S. Pat.No. 6,228,569 and U.S. Ser. No. 09/223,876 hereby incorporated byreference in their entirety. These latter inventions disclose a methodutilizing relatively high heat-set temperatures (>220° C.) appliedduring the film manufacturing process, which substantially improves thefinishing and cutting characteristics of PET-based photographicsupports. However, even with the demonstrated improvements infinishability, the PET-based film is still difficult to cut in varioussteps of the photofinishing process.

[0004] Another general problem with PET film is its tendency to take uphigh levels of curl during storage in cartridges at high temperaturesand its inability to sufficiently lower this curl during photoprocessingas commonly exhibited by CTA-based photographic films. A solution to thelatter problem was proposed in U.S. Pat. No. 5,556,739 to Nakanishi etal., U.S. Pat. No. 5,387,501 to Yajima et al., and U.S. Pat. No.5,288,601 to Greener et al. in which multilayered supports comprisepolyesters modified by sulfonate and other hydrophilic moieties thatfacilitate, in wet processing, recovery of curl imposed on the filmduring storage in a cartridge. Another general approach to lowering thetendency of a polyester film base to take up curl (core-set) duringstorage is through annealing at elevated temperature and/or by raisingthe glass transition temperature (Tg) of the polyester.

[0005] U.S. Pat. No. 3,326,689 to Murayama discloses glow dischargetreatment for improved curl of a film base made from a polyestermaterial, preferably a PEN material. In one case, the polyester materialcomprises a PET-type material in which 25 mol % of the glycol componentrepeat units are derived from CHDM. U.S. Pat. No. 5,294,473 to Kawamotosimilarly discloses a PET polyester film base in which 25 mol % of theglycol component repeat units are derived from CHDM, with improved(reduced) curl.

[0006] U.S. Pat. No. 5,925,507 to Massa et al. discloses a PET film-basematerial having less tendency to core set, comprising polyestercontaining at least 30 weight % 1,4-cyclohexane dimethanol (CHDM), whichpolyester is blended with a polycarbonate that contains bisphenol. U.S.Pat. No. 4,141,735 to Schrader et al. discloses a polyester film basehaving improved core-set curl, involving the use of heat tempering, inone example using poly(1,4-cyclohexylene dimethylene terephthalate).However, this polymer crystallizes rapidly, therefore the making of itsoriented film is difficult. Also, the polymer becomes opaque or hazy anduseless for photographic applications where transparency is required.

[0007] The use of high heat-set temperature during the film-basemanufacturing process has also been used to improve the finishability ofPET-based photographic film. However, even with the demonstratedimprovements in finishability, the PET-based film is still difficult tocut in various steps of the photofinishing process. U.S. Pat. No.5,034,263 to Maier et al. disclosed a laminated film comprising apoly(ethylene terephthalate) core and, on at least one surface thereof,an overcoat of a poly(1,4-cyclohexylene dimethylene terephthalate)polyester, in order to allow the laminated film to be readily slit andperforated using techniques commonly employed with consumer film. Maieret al. states that the CHDM component should comprise at least 70 mol %of the glycol component of the polyester. However, such laminates havebeen found prone to delamination.

[0008] The blending or copolymerizing of conventional polyester withother polyester constituents (polymers or comonomers), in order toimprove the cutting performance of a film, has also been proposed forPEN-based polyester films, as disclosed in U.S. Pat. No. 6,232,054 B1 toOkutu et al. However, PEN is generally considerably more costly and moredifficult to manufacture than PET, so a clear need exists for improvingthe cuttability of PET-based polyester supports.

[0009] Outside the photographic field, poly(ethylene terephthalate)(PET) and poly(ethylene naphthalate) (PEN) are common commercialsemicrystalline polyesters, which are widely used for packagingapplications due to the combination of desirable properties that theypossess. The high oxygen barrier properties of these polyesters renderthem particularly valuable for packaging oxygen-sensitive food and othergoods and materials. PEN has advantages over PET due to its higher Tgand higher oxygen barrier properties, although PEN, as mentioned above,is considerably more costly and is somewhat harder to process than PET.

[0010] The toughness and cutting difficulty of PET and similarpolyesters is generally attributed to the crystal structure andmolecular orientation of the film. It is known that changes in thesefactors, driven either by formulary changes or by modified processconditions, can be used to lower the toughness and improve the cuttingperformance of PET. Generally, the crystallinity of PET can be loweredor altogether eliminated by adding suitable crystallization modifiers.Crystallization modifiers like isophthalic acid (IPA) and1,4-cyclohexane dimethanol (CHDM) are often copolymerized into PET andPEN polyesters to form copolyesters that have better processingproperties. Modest levels of IPA slow down crystallization and raise theoxygen barrier properties. Higher levels of IPA break up crystallinityand lead to amorphous copolyesters with good barrier properties, butthese copolyesters, are known to those skilled in the art, to possesspoor impact and other mechanical properties. Modest levels of CHDM alsoslow down crystallization, but decrease oxygen barrier properties.Higher levels of CHDM are well known to form families of amorphouscopolyesters, which are widely used in commerce in a multitude ofapplications including heavy gauge sheet, signage, medical packages,etc. These copolyesters have excellent impact resistance and othermechanical properties, but have lower oxygen barrier properties thanIPA-modified copolyesters and lower oxygen barrier properties than PET.

[0011] Amorphous copolyesters are generally defined as copolyesters thatdo not show a substantial melting point by differential scanningcalorimetry. These copolyesters are typically based on terephthalicacid, isophthalic acid, ethylene glycol, neopentyl glycol and1,4-cyclohexane dimethanol. It is known that amorphous copolyesterspossess a combination of desirable properties, such as excellent clarityand color, toughness, chemical resistance and ease of processing.Accordingly, such copolyesters are known to be useful for themanufacture of extruded sheets, packaging materials, and parts formedical devices. For example. U.S. Pat. Nos. 5,385,773 and 5,340,907 toYau et al. discloses polyesters of 1,4-cyclohexane dimethanol, in whichthe diol is present in an amount of 10-95 mol % of the glycol component,and a process for producing such copolymers by esterification. U.S. Pat.No. 6,183,848 B1 to Turner et al. disclose an amorphous copolyestercomprising various amounts of comonomers derived from 1,4-cyclohexanedimethanol which, because of improved gas barrier properties, are usefulfor packaging perishable goods. In one embodiment, the copolyester isdisclosed as a biaxially oriented sheet. Film and sheet made fromvarious amorphous PET polyesters comprising repeat units from CHDM aresold by Eastman Chemical Company under the trademark EASTAPAK and EASTARcopolyesters.

[0012] A variety of patents disclose a multilayer film base. Forexample, U.S. Pat. No. 5,034,263 to Maier discloses a multilayer filmbase comprising a core layer of PET. U.S. Pat. No. 5,387,501 to Yajimadiscloses a multilayer film base comprising PET in one layer and asecond layer in which CHDM may be present. U.S. Pat. No. 5,759,756 toLaney discloses a film base comprising a CHDM-containing core. WO01/34391 to Moskala, U.S. Pat. No. 5,288,601 to Greener and U.S. Pat.No. 5,556,739 are further examples of multilayer film bases that maycontain CHDM.

PROBLEM TO BE SOLVED BY THE INVENTION

[0013] Accordingly, it would be desirable to provide a PET film basewith improved physical properties. In particular, it would be desirableto obtain a PET film base that is less tough and better suited forfinishing operations, i.e., slitting, chopping and perforatingprocesses, which are required in the preparation of photographic films.Moreover, it would be desirable to obtain a PET film base that is easierto cut in various steps of the photofinishing process, such as splicing,notching, and sleeving. Additionally, it would be desirable to be ableto use PET as a film base in certain consumer photographic filmapplications and in films processed in a minilab setting. It would alsobe desirable for such a PET film base to have other advantageousproperties such as dimensional stability and a reduced tendency to takeup high levels of curl during storage in cartridges at high temperaturesand/or a higher propensity to lower this curl during photoprocessing.

SUMMARY OF THE INVENTION

[0014] This invention relates to a poly(ethylene terephthalate)photographic film base comprising a multilayer structure, in which acontrolled amount of monomeric units derived from1,4-cyclohexanedimethanol (CHDM) is present in at least two layers, suchthat the multilayer film base has a specified cutting-related property.This can be accomplished either by the addition/blending of polyesterpolymers containing CHDM monomeric units to PET material and/or theincorporation of CHDM monomer units into a PET-polymer backbone atappropriate levels.

[0015] A further embodiment of the invention is directed towards aphotographic element comprising at least one light sensitive silverhalide-containing emulsion layer and a PET multilayer film base producedin accordance with the above embodiments.

[0016] The multilayer film base of the present invention has desirableproperties for use in photographic elements. These include goodstiffness, low tear strength and improved cuttability. Furthermore, amultilayer film base for photographic film or other elements providesexcellent dimensional stability, optical clarity and mechanical strengthin addition to possessing an improved cuttability.

[0017] In the present invention, monomeric units derived from1,4-cyclohexane dimethanol (CHDM) are also referred to as “CHDM repeatunits” or “CHDM-comonomer units.” Other definitions of terms, as usedherein, include the following:

[0018] The term “terephthalic acid,” as used herein is meant to includesuitable synthetic equivalents such as dimethyl terephthalate. It shouldbe understood that “dicarboxylic acids” includes the corresponding acidanhydrides, esters and acid chlorides for these acids. Regarding theglycol/diol component or acid component in the polyester material, themole percentages referred to herein equal a total of 100 mol % each.

[0019] “PET polymer,” “PET resin,” “poly(ethylene terephthalate) resin,”and the like refers to a polyester comprising at least 98 mol %terephthalic-acid comonomer units, based on the total acid component,and comprising at least 98 mol % of ethylene-glycol comonomer units,based on the total glycol component. This includes PET resins consistingessentially of about 100 mol % terephthalic-acid comonomer units, basedon the total acid component, and consisting essentially of about 100 mol% of ethylene-glycol comonomer units, based on the total glycolcomponent.

[0020] The term “modified PET polymer,” “modified PET resin,” or thelike is a polyester comprising at least 70 mol % terephthalic-acidcomonomer units, based on the total acid component, that has beenmodified so that either the acid component is less than 98 mol % ofterephthalic-acid (“TA”) comonomer units or the glycol component is lessthan 98 mol % of ethylene-glycol (“EG”) comonomer units, or both the TAand EG comonomer units are in an amount less than 98 mol %. The modifiedPET polymer is modified with, or copolymerized with, one or morecomonomers other than terephthalic-acid comonomers and/orethylene-glycol comonomers in an amount of greater than 2 mol %(including greater than 5 mol %), of either the acid component and/orthe glycol component, for example, to improve the cuttability of a filmbase or otherwise change the properties of the film base in which it isused. The “modified PET resin” does not necessarily need to contain anyethylene-glycol comonomer units, and it does not necessarily need tocontain any acid component other than terephthalic-acid comonomer units.

[0021] In one preferred embodiment, the “modified PET polymer” is apolyester comprising at least 80 mol % terephthalic-acid comonomerunits, based on the total acid component, and at least 60 mol % ethyleneglycol (EG) comonomer units, further modified with or copolymerized withone or more additional types of comonomers, preferably in the amount ofgreater than 5 mol % of the acid component and/or glycol component.

[0022] The term “CHDM-modified PET” or “CHDM-modified-PET polyester”refers to a modified-PET polymer modified by the inclusion of at least 2mol % (including at least 3.5 mol %) CHDM comonomer units. In onepreferred embodiment, a modified-PET polymer is modified by theinclusion of at least 65 mol % CHDM-comonomer units, based on the totalglycol component.

[0023] Similarly, the term “CHDM-modified polyester” refers to apolyester comprising at least 2 mol % (including at least 3.5 mol %)CHDM-comonomer units, based on total glycol component, but notnecessarily comprising any specific amount of terephthalic acidcomponent. In one embodiment, a CHDM-modified polyester comprises atleast 65 mol % CHDM-comonomer units, based on total glycol component,but not necessarily comprising any specific amount of terephthalic-acidcomonomer units.

[0024] The term “high-CHDM-modified PET” refers to a CHDM-modified PETpolyester in which the level of CHDM-comonomer units is equal to orgreater than 95 mol % (including 100 mol %). This includes both “PCT”(polycyclohexylene dimethylene terephthalate) and “PCTA,” which is acopolymer of three monomers: terephthalic acid, isophthalic acid and1,4-cyclohexane dimethanol, with 100 mol % of the 1,4-cyclohexanedimethanol based on its glycol component.

[0025] The term “high-CHDM-modified polyester” refers to a CHDM-modifiedpolyester in which the level of CHDM-comonomer units is greater than 95mol % (including 100 mol %), but not necessarily comprising any amountof terephthalic-acid comonomer units.

[0026] “PET-based polyester material” is a semicrystalline materialcomprising one or more polymers wherein at least 70 % by weight of thematerial is one or more polymers that are either a PET polymer ormodified PET polymer. Optionally, the material may also include addendasuch as silica beads, plasticizers and the like.

[0027] A film base is made using a PET-based polyester material in thepresent invention. In one embodiment, preferably greater than 80 % byweight, more preferably greater than 90 % by weight, of the PET-basedpolyester material used in this invention is one or more polymers thatare either a PET polymer or modified PET polymer.

DETAILED DESCRIPTION OF THE INVENTION

[0028] As indicated above, one aspect of the present invention isdirected to an imaging element comprising at least one light-sensitiveor heat-sensitive imaging layer over a support that comprises abiaxially stretched, semicrystalline multilayer film base comprising atleast two layers.

[0029] In one embodiment, a main or first layer, adjacent a secondlayer, is made of a first PET-based polyester material comprising one ormore polyester resins, in which material the total level of repeat unitsderived from 1,4-cyclohexane dimethanol is at least 3.5 mol % based ontotal glycol component in the material except that in the case of theadjacent second layer having a level of repeat units derived from1,4-cyclohexane dimethanol that is between 3.5 and 25 mol %, based ontotal glycol component in the material, then the first layer can haveless than 3.5 mol %,or none at all, that is, can consist of PET polymer.Adjacent on at least one side of the first layer, the second layer ismade of a second PET-based polyester material comprising one or morepolyester resins, in which material the total level of repeat unitsderived from 1,4-cyclohexane dimethanol is greater than the mol % in thefirst layer, based on total glycol component in the material, andwherein the difference in the level of 1,4-cyclohexane dimethanolbetween said layers is less than 50 mol % based on the glycol component.At least the polyester material in the second layer is semi-crystalline.Such a film base, typically having a total thickness of 50 to 180 μm,has a cutting index, as defined in equations 1 and 2 below, of less than4.2.

[0030] The multilayer film base can consist of only two layers, a firstlayer and a second layer, or the film base can comprise three or morelayers. In the case of a three-layer multilayer film base, a thirdlayer, on the opposite side of the first layer from second layer, cancomprise a third PET-based polyester material comprising one or morepolyester resins, in which material the total level of repeat unitsderived from 1,4-cyclohexane dimethanol is greater than the level in thefirst layer, based on total glycol component in the material, whereinthe difference in the level of 1,4-cyclohexane dimethanol between themain layer and any adjacent layer is less than 50 mol % of the totalglycol component, and wherein the composition of the second and thirdlayers can be the same or different. In the case of a multilayer filmbase comprising three layers, the first layer can be referred to as acore layer and the second and third layers can be referred to,respectively, as a first and a second outer or surface layer.

[0031] As indicated above, the thickness of the first layer can begreater than any other layer. Preferably, the thickness ratio of thefirst layer to the entire film base is 0.30 to 0.95, more preferably0.40 to 0.85. Preferably, in the case of a two-layer film base, theratio is between 0.5 to 0.95. Similarly, the ratio of the thickness ofthe second layer to the thickness of the entire film base is preferably0.05 to 0.70.

[0032] By the term “main layer” is meant that the layer providessubstantial stiffness to the film base and in some cases, but notnecessarily, the layer is thicker than other layers in the multilayerfilm base. In one particular embodiment, involving one or two otherlayers, the ratio of the thickness of said main layer to the sum of theother layers in the multilayer film base is 0.5 to 20.

[0033] In one embodiment of the present invention, the second layercomprises a first PET-based polyester material in which the total levelof repeat units derived from 1,4-cyclohexane dimethanol is 3.5 to 25 mol% based on total glycol component in the material, and the main layercomprises a lesser amount, or an absence of any, 1,4-cyclohexanedimethanol, based on total glycol component in the material. Thisembodiment, relative to the next embodiment, involves a relatively lowamount of 1,4-cyclohexane dimethanol in the second layer.

[0034] Another embodiment of a film base according to the presentinvention involves a film base having a main layer that comprises afirst PET-based polyester material in which the total repeat unitsderived from 1,4-cyclohexane dimethanol is at least 10 mol % based ontotal glycol component in the material; and an outer or second layer ofa second PET-based polyester material that comprises greater than 60 mol% of repeat units derived from 1,4-cyclohexane dimethanol, based ontotal glycol component in the material, and wherein the difference inthe level of 1,4-cyclohexane dimethanol between the core layer and anyadjacent layer is less than 50 mol % of the total glycol component. Thisembodiment involves a relatively high amount of 1,4-cyclohexanedimethanol in the second layer.

[0035] Preferably, in such an embodiment, the level of repeat unitsderived from 1,4-cyclohexane dimethanol in the main layer is in therange of about 10 to 22 mol %, based on total glycol component in thematerial, and the cutting index of said multilayer film base (as definedin equations 1 and 2 below) is less than 3.5.

[0036] The PET-based polyester material in the first layer can be amiscible blend of at least two polyesters, for example, a firstpolyester that is a PET polymer or a modified-PET polymer and a secondpolyester, the second polyester comprising repeat units derived from1,4-cyclohexane dimethanol such that the total repeat units derived from1,4-cyclohexane dimethanol in the polyester material is at a levelbetween 3.5 to 25 mol % based on total glycol component in the polyestermaterial.

[0037] Similarly, in one embodiment of the invention, the PET-basedpolyester material in the second layer can comprise a miscible blendcomprising at least two polyesters, for example, a first polyester thatis a high-CHDM-modified PET polyester in which the level ofCHDM-comonomer units is above about 95 mol %, and a second polyestercomprising repeat units derived from 1,4-cyclohexane dimethanol, whereinthe total repeat units derived from 1,4-cyclohexane dimethanol in thePET-based polyester material is at a level of 60 to 100 mol %,preferably 65 to 100 mol %, based on total glycol component in thepolyester material.

[0038] Some specific examples of multilayer film bases include the casewhere the first layer is a CHDM-modified polyester and the second layeris a polyester comprising 100 mol % 1,4-cyclohexane dimethanol based onits glycol content. Analogously, in the case of a three-layer film base,the core layer can be a CHDM-modified polyester and both outer layerscan consist of a polyester comprising 100 mol % 1,4-cyclohexanedimethanol based on its glycol content.

[0039] In accordance with another embodiment of the invention, a PETresin is blended using a suitable compounding method with aCHDM-modified-PET polyester containing CHDM comonomer at a sufficientlevel, and this blend is then used to prepare a biaxially stretched andheat-set film or sheet material under conditions similar to those usedfor preparing conventional PET film. In still another embodiment of thisinvention, a modified-PET resin comprising CHDM comonomer at asufficient level is used to prepare a biaxially stretched and heat-setfilm or sheet material under conditions similar to those used forpreparing conventional PET film.

[0040] As indicated above, in one embodiment of the photographicmultilayer film base according to the present invention, the main layercan be made from a PET-based polyester material comprising one or morepolyester resins, in which material the level of repeat units derivedfrom 1,4-cyclohexane dimethanol (CHDM) can be between 3.5 and 25 mol %,based on total glycol component in the material, such that the cuttingindex (as defined in Equations 1 and 2 below) of said multilayer filmbase is less than 4.2. Preferably, in such a case, the multilayer filmbase comprises a material in which the level of repeat units derivedfrom 1,4-cyclohexane dimethanol is between 5 and 22 mol %, based ontotal glycol component in the material, and the cutting index of saidmultilayer film base is less than 3.5. Also, preferably, less than 25mol % of the total glycol component are aromatic, more preferably lessthan 10 mol %, most preferably essentially zero mol %.

[0041] In the case of a blend, the main layer of the multilayer filmbase of the present invention can comprise a polyester materialcomprising at least two polyesters, a first polyester that is a PETpolymer or a modified-PET polymer that is blended with a secondpolyester, the second polyester comprising repeat units derived from1,4-cyclohexane dimethanol such that the total repeat units derived from1,4-cyclohexane dimethanol in the polyester materials is at a levelbetween 3.5 and 25 mol % based on total glycol component in thepolyester materials. In one embodiment, the first polyester may have norepeat units from 1,4-cyclohexane dimethanol and/or the second polyestermay be a modified-PET polyester. In another embodiment, the secondpolyester may have no repeat units derived from terephthalic acid or itsester.

[0042] Preferably, the multilayer film base comprising the PET-basedpolyester material has a cutting index (see equations 1 and 2 below) ofless than 3.5, more preferably less than 3.0.

[0043] Preferably, the Tg of the polymers in the polyester material inat least the first and second layer, preferably all layers, of themultilayer film base according to the present invention is less than 90°C.

[0044] The CHDM-modified-PET polyesters used in making the articles ofthis invention preferably have about 100 mol % of a dicarboxylic acidportion and about 100 mol % of a glycol portion. Less than about 30 mol%, preferably not more than about 20 mol % of the dicarboxylic acidrepeat units may be from other conventional acids such as those selectedfrom succinic, glutaric, adipic, azaleic, sebacic, fumaric, maleic,itaconic, 1,4-cyclohexane-dicarboxylic, phthalic, isophthalic, andnaphthalene dicarboxylic acid.

[0045] Preferably, the glycol component of the CHDM-modified-PETpolyesters contain repeat units from between 3.5 and 50 mol % of1,4-cyclohexane-dimethanol and about 96.5 to 50 mol % of ethyleneglycol. The glycol component may optionally include less than 35 mol %,preferably not more than about 10 mol % of other conventional glycolssuch as propylene glycol, 1,3-propanediol;2,4-dimethyl-2-ethylhexane-1,3-diol, 2,2-dimethyl-1,3-propanediol,2-ethyl-2-butyl- 1,3 -propanediol, 2-ethyl-2-isobutyl- 1,3 -propanediol,1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol,1,6-hexanediol, 1,8-octanediol, 2,2,4-trimethyl-1,6-hexanediol,thiodiethanol, 1,2-cyclohexane dimethanol, 1,3-cyclohexane dimethanol,2,2,4,4-tetramethyl-1,3-cyclobutanediol, polyethylene glycol of variousmolecular weights and the like.

[0046] In one embodiment of the invention, the CHDM-modified-PETpolyesters used in the multilayer film base comprise copolyesters havinga dicarboxylic acid component and a glycol component, the dicarboxylicacid component comprising repeat units from at least 80 mol %terephthalic acid (or its ester) and the glycol component comprisingless than 25 mol %, preferably between about 3.5 and 25 mol %, of repeatunits from 1,4-cyclohexane dimethanol and about 96.5 to 75 mol % fromanother glycol, preferably from ethylene glycol.

[0047] In the case of embodiments involving blends, a blend comprisingat least two polyesters, wherein at least one PET polymer and/or amodified-PET polymer is blended with a CHDM-modified polyester,preferably a CHDM-modified PET polyester, such that the level of theCHDM-comonomer units in the total blend is between 3.5 and 25 mol %,preferably less than 22 mol %, more preferably less than 20 mol %. Inthe CHDM-modified polyester, any of the above-mentioned acid componentsmay be used and any of the above-mentioned glycol components may be usedin addition to the CHDM component.

[0048] In one embodiment, a preferred CHDM-modified PET for use in thepresent invention, in one or more layers of the film base, isrepresented by the following structure:

[0049] In Structure (I) above, the subscripts x and y represent the mol%, based on the total glycol component of the comonomer. Other acid orglycol monomers may be substituted to the extent described above.

[0050] Preferably, in one embodiment, a miscible blend for use in afirst layer of the multilayer base film comprises a PET polymer and aCHDM-modified polymer in the ratio of 95:5 to 5:95 more preferably 85:15to 10:90. Preferably, the mol % of the CHDM-comonomer units relative tothe total glycol component in the CHDM-modified polymer is 3.5% to 35mol %. Preferably, the acid component in the CHDM-modified polymer is80% to 100% of terephthalic acid component.

[0051] As indicated above, in one embodiment of the invention, a secondor outer layer comprises a high-CHDM-modified PET resin that is blended,using a suitable compounding method, with a polyester containingCHDM-comonomer units at a sufficient level. This resin is then used toprepare a biaxially stretched and heat-set film under conditions similarto those used for preparing PET film base. In another embodiment of thisinvention, the modified-PET resin comprising CHDM comonomer at asufficient level is used to prepare a biaxially stretched and heat-setfilm under conditions similar to those used for preparing PET film base.Typically, biaxially stretching the material causes amorphous materialto become semicrystalline. In a typical embodiment, the crystallinity isat least 10%.

[0052] More particularly, in one embodiment of the present invention, asecond layer or one or more outer layers of a photographic film baseaccording to the present invention comprises a PET-based polyestermaterial comprising one or more polyester resins, in which material thelevel of repeat units derived from 1,4-cyclohexane dimethanol (CHDM) isoverall 60 to 100 mol %, preferably 65 to 95 mol %, based on totalglycol component in the material, such that the cutting index (asdefined in Equations 1 and 2 below) of said film base is less than 4.2,preferably less than about 3.5. Preferably, in such a case, the secondor outer layers of the film base comprises a material in which the levelof repeat units derived from 1,4-cyclohexane dimethanol is 70 to 95 mol%, based on total glycol component in the material, and the cuttingindex of said film base is less than 4.2, preferably less than 3.5.Also, preferably, less than 25 mol % of the total glycol units arearomatic.

[0053] In the case of a blend, the second or outer layer of the filmbase of the latter embodiment of the present invention comprises apolyester material comprising a first polyester that is ahigh-CHDM-modified PET polymer that is blended with a second polyester,the second polyester comprising repeat units derived from1,4-cyclohexane dimethanol such that the total repeat units derived from1,4-cyclohexane dimethanol in the polyester materials is at a levelbetween 65 to 100 mol % based on total glycol component in thepolyester. All polyester materials in the blend must be miscible, thatis, the film produced from said blend must be optically clear, to meetthe stringent optical requirements of high transparency and low hazeplaced on photographic film bases. Preferably, the repeat units derivedfrom 1,4-cyclohexane dimethanol in the material of second layer of thisembodiment are at a level of greater than 70, more preferably greaterthan 75 mol % based on total glycol component in the polyester.

[0054] The CHDM-modified-PET polyesters used in making the articles ofthis invention preferably have about 100 mol % of a dicarboxylic acidportion and about 100 mol % of a glycol portion. Less than about 20 mol%, preferably not more than about 10 mol % of the dicarboxylic acidrepeat units may be from other conventional acids such as those selectedfrom succinic, glutaric, adipic, azelaic, sebacic, fumaric, maleic,itaconic, 1,4-cyclohexane-dicarboxylic, phthalic, isophthalic, andnaphthalene dicarboxylic acid.

[0055] Preferably, the glycol component of the CHDM-modified-PETpolyesters used in one embodiment of the present invention, in whichthere is a relatively high level of 1,4-cyclohexane dimethanol in theouter layer or layers, contain repeat units comprising from 65 to 100mol % of 1,4-cyclohexane dimethanol and from about 5 to 35 mol % ofethylene glycol. The glycol component may optionally include less than35 mol %, preferably not more than about 10 mol % of other conventionalglycols such as propylene glycol, 1,3-propanediol;2,4-dimethyl-2-ethylhexane-1,3-diol, 2,2-dimethyl-1,3-propanediol,2-ethyl-2-butyl-1,3 -propanediol, 2-ethyl-2-isobutyl-1,3 -propanediol,1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol,1,6-hexanediol, 1,8-octanediol, 2,2,4-trimethyl-1,6-hexanediol,thiodiethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol,2,2,4,4-tetramethyl-1,3-cyclobutanediol and the like.

[0056] Another embodiment of the invention involves a film base made ofa PET-based polyester material in one of the layers, preferably thesecond or outer layers, comprising one or more polyester resins, inwhich material the level of repeat units derived from 1,4-cyclohexanedimethanol, based on the total glycol component, is 65 to 100 mol %, andthe level of repeat units derived from an acid component other thanterephthalic acid or its ester is in the amount of 3 to 30 mol %,preferably 5 to 20, based on the total acid component, and wherein thecutting index of the film base is less than 4.6, preferably less than4.2, more preferably less than 3.5, most preferably less than 2.0.

[0057] The acid component other than terephthalic acid can, for example,isophthalic acid (IPA), dimethyl isophthalate,1,4-cyclohexanedicarboxylic acid (1,4-CHDA), 1,4 cyclohexanediaceticacid, diphenyl-4,4-dicarboxylic acid,dimethyl-2,6-naphthalene-dicarboxylate, succinic acid, glutaric acid,adipic acid, azelaic acid, sebacic acid, paraphenylenedicarboxylic acid(PPDA), naphthalcnedicarboxylic acid (NDA), and mixtures thereof.Preferably, the other acid component is isophthalic acid (IPA),1,4-cyclohexanedicarboxylic acid (1,4-CHDA), paraphenylenedicarboxylicacid (PPDA), naphthalenedicarboxylic acid (NDA), and the like, andmixtures thereof.

[0058] As indicated above, the multilayer film base is useful in aphotographic element comprising at least one silver-halide imaging layerover a support comprising a multilayer film base. Such a photographicelement can be a photographic film or a photothermographic film.

[0059] In addition to the PET-based layer or multilayer film baseaccording to the present invention, the support can further comprise oneor more photographically acceptable subbing layers, backing layers, tielayers, magnetic layers and the like.

[0060] Subbing layers are used for the purpose of providing an adhesiveforce between the polyester support and an overlying photographicemulsion comprising a binder such as gelatin, because a polyester filmis of a very strongly hydrophobic nature and the emulsion is ahydrophilic colloid. If the adhesion between the photographic layers andthe support is insufficient, several practical problems arise such asdelamination of the photographic layers from the support at the cutedges of the photographic material, which can generate many smallfragments of chipped-off emulsion layers which then cause spot defectsin the imaging areas of the photographic material.

[0061] Various subbing processes and materials have, therefore, beenused or proposed in order to produce improved adhesion between thesupport film and the hydrophilic colloid layer. For example, aphotographic support may be initially treated with an adhesion promotingagent such as, for example, one containing at least one of resorcinol,catechol, pyrogallol, 1 -naphthol, 2,4-dinitro-phenol,2,4,6-trinitrophenol, 4-chlororesorcinol, 2,4-dihydroxy toluene,1,3-naphthalenediol, 1,6-naphthalenediol, acrylic acid, sodium salt of1-naphthol-4-sulfonic acid, benzyl alcohol, trichloroacetic acid,dichloroacetic acid, o-hydroxybenzotrifluoride,m-hydroxybenzotrifluoride, o-fluorophenol, m-fluorophenol,p-fluorophenol, chloralhydrate, and p-chloro-m-cresol. Polymers are alsoknown and used in what is referred to as a subbing layer for promotingadhesion between a support and an emulsion layer. Examples of suitablepolymers for this purpose are disclosed in U.S. Pat. Nos. 2,627,088;2,968,241; 2,764,520; 2,864,755; 2,864,756; 2,972,534; 3,057,792;3,071,466; 3,072,483; 3,143,421; 3,145,105; 3,145,242; 3,360,448;3,376,208; 3,462,335; 3,475,193; 3,501,301; 3,944,699; 4,087,574;4,098,952; 4,363,872; 4,394,442; 4,689,359; 4,857,396; British PatentNos. 788,365; 804,005; 891,469; and European Patent No. 035,614. Oftenthese include polymers of monomers having polar groups in the moleculesuch as carboxyl, carbonyl, hydroxy, sulfo, amino, amido, epoxy or acidanhydride groups, for example, acrylic acid, sodium acrylate,methacrylic acid, itaconic acid, crotonic acid, sorbic acid, itaconicanhydride, maleic anhydride, cinnamic acid, methyl vinyl ketone,hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxychloropropylmethacrylate, hydroxybutyl acrylate, vinylsulfonic acid, potassiumvinylbenezensulfonate, acrylamide, N-methylamide, N-methylacrylamide,acryloylmorpholine, dimethylmethacrylamide, N-t-butylacrylamide,diacetonacrylamide, vinylpyrrolidone, glycidyl acrylate, orglycidylmethacrylate, or copolymers of the above monomers with othercopolymerizable monomers. Additional examples are polymers of, forexample, acrylic acid esters such as ethyl acrylate or butyl acrylate,methacrylic acid esters such as methyl methacrylate or ethylmethacrylate or copolymers of these monomers with other vinylicmonomers; or copolymers of polycarboxylic acids such as itaconic acid,itaconic anhydride, maleic acid or maleic anhydride with vinylicmonomers such as styrene, vinyl chloride, vinylidene chloride orbutadiene, or trimers of these monomers with other ethylenicallyunsaturated monomers. Materials used in adhesion-promoting layers oftencomprise a copolymer containing a chloride group such as vinylidenechloride.

[0062] The composition of the PET-based polyester material comprisingthe two or more layers of the multilayer film base of the presentinvention can be made by conventional processes. In general, as is wellknown by the skilled artisan, polyesters comprise the reaction productof at least one dicarboxylic acid and at least one glycol component. Thedicarboxylic acid component can typically comprise residues ofterephthalic acid, isophthalic acid, 1,4-cyclohexanedicarboxylic acid,2,6-naphthalenedicarboxylic acid, and/or mixtures thereof. Also suitableare the anhydrides thereof, acid chlorides thereof, and lower, e.g.,C1-C8 alkyl esters thereof. Any isomers of the dicarboxylic acidcomponent or mixtures thereof may be used. For example, cis, trans, orcis/trans mixtures of 1,4-cyclohexanedicarboxylic acid may be employed.Examples of suitable naphthalene dicarboxylic acid isomers include1,4-naphthalenedicarboxylic acid, 2-6-naphthalenedicarboxylic acid,2,7-naphthalenedicarboxylic acid or mixtures thereof.

[0063] The polyester polymers used in the present invention can beprepared by a process comprising reacting the dicarboxylic acidcomponent and the glycol component at temperatures sufficient to effectesterification or ester exchange and polycondensing the reaction productunder an absolute pressure of less than 10 mm Hg for a time of less thanabout 2 hours in the presence of a catalyst and inhibitor system. Anexample of a preferred catalyst and inhibitor system is about 0-75 ppmMn, about 50-150 ppm Zn, about 5-200 ppm Ge, about 5-20 ppm Ti and about10-80 ppm P, all parts by weight based on the weight of the copolyester.

[0064] Either dimethyl terephthalate (or other lower dialkylterephthalate ester) or terephthalic acid can be used in producing thecopolyester. Thus, the term “terephthalic acid component, monomer,repeat unit, or portion” herein is meant to include either the acid orester form. These materials are commercially available. The glycols CHDMand ethylene glycol are also commercially available. Either the cis ortrans isomer of CHDM, or mixture thereof, may be used in accordance withthe present invention.

[0065] Generally, the copolyesters may be produced using conventionalpolyesterification procedures described, for example, in U.S. Pat. Nos.3,305,604 and 2,901,460, the disclosures of which are incorporatedherein by reference. The amorphous or semi-crystalline copolyestersaccording to the invention are prepared by conventional polymerizationprocesses known in the art, such as disclosed by U.S. Pat. Nos.4,093,603 and 5,681,918, the disclosures of which are hereinincorporated by reference. Examples of polycondensation processes usefulin making the PET material of the present invention include melt phaseprocesses conducted with the introduction of an inert gas stream, suchas nitrogen, to shift the equilibrium and advance to high molecularweight or the more conventional vacuum melt phase polycondensations, attemperatures ranging from about 240° C. to about 300° C. or higher whichare practiced commercially. Although not required, conventionaladditives may be added to the copolyester materials of the invention intypical amounts. Such additives include pigments, colorants,stabilizers, antioxidants, extrusion aids, slip agents, carbon black,flame retardants and mixtures thereof.

[0066] Various modified-PET polyesters comprising repeat units fromCHDM, which can be used in the present invention, are commerciallyavailable from Eastman Chemical Company (Kingsport, Tenn.) under thetrademark EASTAPAK and EASTAR copolyester, as described athttp://www.eastman.com.

[0067] Photographic elements of this invention can have the structuresand components shown in Research Disclosure Item 37038 and can beimagewise exposed and processed using known techniques and compositions,including those described in the Research Disclosure Item 37038 citedabove.

[0068] The multilayer film base may be manufactured by a process ofcasting, biaxial stretching and heat-setting. The process for making PETmultilayer film base typically comprises the steps of coextruding andcasting the molten film base onto a casting surface along the machinedirection to form a continuous sheet, drafting the sheet by stretchingin the machine direction, tentering the sheet by stretching in thetransverse direction, heat-setting the drafted and tentered sheet, andcooling the heat-set sheet to form a stretched, heat-set PET film, suchas described in, e.g., U.S. Pat. No. 4,141,735 to Schrader et al., thedisclosure of which is incorporated in its entirety by reference herein.Alternately, the stretching of the film in the machine and transversedirections can be performed simultaneously using appropriate machinery.

[0069] In one particular embodiment, the process for preparing filmsfrom the resin compositions of this invention comprises the followingsteps:

[0070] (1) The resins are fed by two plasticating extruders into amulti-manifold co-extrusion sheet-forming die and are cast under moltenconditions onto a cooling surface to form a continuous cast sheet.Preferably, the molten polyester resins have an inherent viscosity offrom 0.5 to 0.8 dl/g, and are cast at temperatures of from 250 to 310°C. while the casting surface has a temperature of from 40 to 70° C. Theinherent viscosity (IV) is measured at 25° C. in a solvent mixture ofphenol/chlorobenzene (60/40 by weight) at a concentration of 0.25 g/dlwith an Ubbelhode glass viscometer.

[0071] (2) The continuous multilayer sheet is removed from the castingsurface and passed into a drafting zone where it is first preheated andthen stretched in the machine direction at a stretch ratio of 2.0 to4.0, at a temperature of from about 80° C. to 110° C. The drafting zonetypically includes two sets of nipped rollers, the first being theentrance to the drafting zone and the second the exit from the draftingzone. To achieve the stretch ratios necessary for the practice of thisinvention, the exit nip rollers are rotated at a speed greater than theentrance nip rollers. The film may be cooled in the last stage of thedrafting zone to 25° C. to 40° C.

[0072] (3) The film moves from the drafting zone into a tentering zonewhere it is preheated and stretched in the transverse direction at astretch ratio of 2.0 to 4.0, at a temperature of from about 80° C. to115° C. The tentering zone typically includes a means for engaging thefilm at its edges and stretching such that the final width is from 2.0to 4.0 times that of the original width.

[0073] (4) The film is next heat-set by maintaining it at a temperatureof at least 200° C., but below the melting point of the resin having thelowest melting transition in the multilayer sheet, preferably at least200° C. to 240° C., while being constrained as in the tentering zone fora time sufficient to affect heat-setting. Times longer than necessary tobring about this result are not detrimental to the film; however, longertimes are undesired as the lengthening of the zone requires highercapital expenditure without achieving additional advantage. Theheat-setting step is typically accomplished within a time period of 0.1to 15 seconds and preferably 0.1 to 10 seconds. Finally, the film iscooled without substantial detentering (the means for holding the edgesof the film do not permit greater than 2% shrinkage thereof).

[0074] Preferably, in order to improve its dimensional stability andlower its core-set propensity, the multilayer film base is heat treatedat temperatures of from 50° C. up to Tg(H) for times ranging from 1 hrto 1000 hrs, where Tg(H) is the glass transition temperature of thepolyester material in the multilayer film having the highest glasstransition temperature.

[0075] With regard to cuttability, it is generally known in the art ofsheet material cutting that the cutting process combines crack formationand propagation. To form a crack, one needs to apply cutters to causecompression on the surfaces of the sheet material until the material isdeformed and its break point is reached. Once the material's break pointis reached, a crack would be formed, which starts the second stage ofcutting—crack propagation. One can maintain and eventually complete thecutting process by compressing the sheet material further using thecutters. Eventually, the cutting would be completed as cracks propagatethrough the sheet thickness.

[0076] To evaluate the cuttability of a given material, one needs toevaluate how the material behaves during the crack formation andpropagation stages. If the material absorbs and dissipates moremechanical energy during the crack formation and propagation processes,it is said to be more difficult to cut and will have a lowercuttability. Two standard tests can be used to evaluate how muchmechanical energy a material absorbs and dissipates during the saidcrack formation and propagation steps. One is the tensile test (ASTMD882) and the other is the tear test (ASTM D1938). The former can beused to evaluate the crack formation part of the cutting process, andthe latter can be used to assess the crack propagation part of thecutting process.

[0077] The mechanical and cutting properties of the polyester films ofthe present invention were evaluated in accordance with the followingprocedures:

[0078] Tensile Properties: Modulus and tensile toughness can bedetermined using a tensile test such as that described in ASTM D882. Atensile test consists of pulling a sample of material with a tensileload at a specified rate until it breaks. The test sample used may havea circular or a rectangular cross section. From the load and elongationhistory, a stress-strain curve is obtained with the strain being plottedon the x-axis and stress on the y-axis. The modulus is defined as theslope of the initial linear portion of the stress-strain curve. Themodulus is a measure of the stiffness of the material. The tensiletoughness is defined as the area under the entire stress-strain curve upto the fracture point. The tensile toughness is a measure of the abilityof a material to absorb energy in a tensile deformation. Both modulusand tensile toughness are fundamental mechanical properties of thematerial.

[0079] Tear Strength: The resistance to tear can be determined using atear test such as that described in ASTM D 1938. The test measures theforce to propagate tearing in a fracture mode III. The test sample usedhas a rectangular shape and a sharp long cut in the middle. Theseparated two arms are then fixed in a conventional testing machine suchas Instron®. The fixtures move at constant speed to prolong thepreexisting cut and the steady state force of tearing is recorded.

[0080] Cutting Index: It is generally known that tensile toughnessrepresents the energy required to initiate a crack, while fracturetoughness determines the energy needed to further propagate the crack.As typical cutting processes involve both crack initiation and crackpropagation, a quantity of cuttability can be defined based on these twofundamental material quantities. Tensile toughness can be evaluatedthrough tensile testing. Fracture toughness G_(c) can be calculated fromthe tear strength:

G _(c)=2P _(c) /b  (1)

[0081] where P_(c) is the load at tear crack growth and b is thespecimen thickness. (See Rivlin, R. S. & Thomas, A. G., (1953), J.Polym. Sci., 10, 291).

[0082] For practical simplicity, a dimensionless quantity of cuttingindex is defined as follows,

C=0.5*W _(t) /W _(tr)+0.5*G _(c) /G _(cr)  (2)

[0083] where C is the cutting index, W_(t) is tensile toughness andG_(c) is fracture toughness, and W_(tr) and G_(cr) are the correspondingproperties of a reference material, where CTA is selected as thereference material of this invention. The cutting indices of commonlyused film base materials such as PET, PEN and CTA correspond well totheir practical cutting performance. Generally, it is desirable for C tobe close to 1 (CTA value).

[0084] The polyester films having the properties set forth above andprepared by the process described above are less likely to fail and morelikely to produce cleaner cut surfaces in various cutting operations. Infact, the films prepared in accordance with this invention comparefavorably with CTA, which has been the film base of choice for a longtime in the photographic industry because of its special physicalcharacteristics.

The present invention is described in greater detail below by referringto the Examples. However, the present invention should not be construedas being limited thereto. EXAMPLES

[0085] Materials:

[0086] The poly(ethylene terephthalate) (PET)-based supports in thefollowing examples were prepared using the following materials:

[0087] Polyester-1 (P-1): EASTAPAK PET Polyester 7352 (Trademark ofEastman Chemical Company, USA) is a PET resin.

[0088] Polyester-2 (P-2): EASTAR Copolyester 15086 (Trademark of EastmanChemical Company, USA) is a CHDM-modified PET resin comprisingapproximately 12 mol % of 1,4-cyclohexane dimethanol (CHDM) monomerunits of its glycol component.

[0089] Polyester-3 (P-3): EASTAR Copolyester 6763 (Trademark of EastmanChemical Company, USA) is a CHDM-modified PET polyester comprisingapproximately 31 mol % of CHDM monomer units of its glycol component.

[0090] Polyester-4 (P-4): EASTAR Copolyester 5445 (Trademark of EastmanChemical Company, USA) is a CHDM-modified PET polyester comprisingapproximately 62 mol % of CHDM monomer units of its glycol component.

[0091] Polyester-5 (P-5): EASTAR A150 (Trademark of Eastman ChemicalCompany, USA) is a high-CHDM-modified PET polyester comprisingapproximately 17 mol % isophthalic acid of its total acid component and100 mol % of CHDM of its total glycol component.

[0092] Polyester-6 (P-6): EASTAPAK PET (Trademark of Eastman ChemicalCompany, USA) and EASTAR Copolyester 6763 (Trademark of Eastman ChemicalCompany, USA) were mixed at a weight ratio of 32:68, dried at 66° C. for24 hours and then melt-kneaded and extruded at 277° C. using a twinscrew extruder, resulting in a blend comprising approximately 21 mol %CHDM of its total glycol component.

[0093] Polyester-7 (P-7): EASTAR Copolyester 5445 (Trademark of EastmanChemical Company, USA) and EASTAR A150 (Trademark of Eastman ChemicalCompany, USA) were mixed at a weight ratio of 77:23, dried at 66° C. for24 hours and then melt-kneaded and extruded at 277° C. using a twinscrew extruder, resulting in a blend comprising approximately 70 mol %CHDM of its total glycol component.

Example 1

[0094] P-4 and P-3 resins were used to form a two-layer film via aprocess of melt co-extrusion and biaxial stretching. The resins wereextruded from two single-screw extruders through a sheet-formingco-extrusion die at about 280° C. The sheet was cast onto a coolingsurface at about 60° C. to form a continuous two-layered cast sheet.After removal from the cooling surface the sheet was drafted andtentered at about 95° C. to about 3.4 times its original dimensions inthe machine and transverse directions. The resulting film was 70 μmthick, having a layer thickness ratio of 1:3.7 with P-3 comprising thethicker, main layer in the two-layer film.

Example 2

[0095] The process of Example 1 was repeated except that P-2 resin wasco-extruded with P-1 resin to form a two-layered laminate. The polymerresins were extruded at about 280° C. The laminate was drafted andtentered at about 95° C. to about 3.4 times its original dimensions inthe machine and transverse directions. The resulting film was 70 □mthick, having a layer thickness ratio of 1:3.7 with P-1 comprising thethicker, main layer in the two-layer film.

Example 3

[0096] The process of Example 1 was repeated except that P-5 resin wasco-extruded with P-4 resin to form a two-layered laminate. The polymerswere extruded at about 280° C. The laminate was drafted and tentered atabout 102° C. to about 3.4 times its original dimensions in the machineand transverse directions. The resulting film was 70 □m thick, having alayer thickness ratio of 1:3.7 with P-4 comprising the thicker, mainlayer in the two-layer film.

Example 4

[0097] The process of Example 1 was repeated except that P-7 resin wasco-extruded with P-6 resin to form a three-layered laminate The polymerresins were extruded at about 280° C. The laminate was drafted andtentered at about 99° C to about 3.4 times its original dimensions inthe machine and transverse directions. The resulting film was 70 □mthick, having a layer thickness ratio of 1:3.7 with P-6 comprising thethicker, main layer in the two-layer film.

Comparative Example 1

[0098] P-1 resin was converted into film using the process of meltextrusion and biaxial stretching. The resin was extruded at about 280°C. through the sheet-forming co-extrusion die used in the above examplesand cast onto a cooling surface at about 60° C. to form a continuouscast sheet with a homogeneous composition. The laminate was drafted andtentered at about 100° C to about 3.4 times its original dimensions inboth the machine and transverse directions.

Comparative Example 2

[0099] Comparative Example 2 is a conventional cellulose triacetate(CTA) film used as a support for traditional 35 mm photographicelements. This film is traditionally manufactured by a solvent-castingprocess.

[0100] Physical Property Evaluation: The tensile toughness, tearresistance and post-process curl of the films prepared in the aboveexamples were measured according to the following the procedures.

[0101] Tensile Toughness: All tests are performed in accordance withASTM D 882-80a in a standard environment of 50% RH and 23° C. Thetensile test is conducted using a Sintech®2 mechanical testing systemwith Testworks® version 4.5 software. The specimen size is 1.5 cm wideby 10.2 cm long (gauge length). The crosshead speed is 5.1 cm/min. Fivespecimens are tested per film sample. The reported tensile toughness isthe area under the stress-strain curve.

[0102] Tear Strength: All tear tests are performed in accordance withASTM D1938 in a standard environment of 50% RH and 23° C. The tear testis conducted using a Sintech®2 mechanical testing system with Testworks®version 4.5 software. The specimen size is 2.5 cm wide by 7.6 cm long. A2.5 cm long cut is first made in the specimen at the center of the widthusing a pair of sharp scissors, creating two distinct arms. The arms areplaced between two flat-faced grips of the mechanical test frame andstretched apart. The crosshead speed is 25 cm/min. The tear strength isreported by normalizing the average peak load by the thickness of thefilm.

[0103] The key properties of the test films prepared in the examples ofthe present invention are listed in Table 1 below. The cutting index wasdetermined according to Equation 2 above. TABLE 1 Polyester PolyesterTensile Tear in Outer in Main toughness strength Cutting Example NoLayer Layer MPa g/100□m index 1 P-4 P-3 49 17 1.4 2 P-2 P-1 102 34 2.9 3P-5 P-4 22 7 0.6 4 P-7 P-6 43 26 1.5 Comparative — P-1 131 81 4.5 1Comparative — CTA 23 25 1.0 2

[0104] As shown in Table 1, the film sample of Comparative Example 1 isexpected to have poor cutting performance in various photofinishingoperations because of its high cutting index. By contrast, themultilayer film samples of Examples 1-4 comprising CHDM-modifiedpolyester material are expected to have improved cutting performance,much closer to the performance of standard CTA film (Comparative Example2), since the corresponding cutting indices are comparatively lower andmuch closer to 1.

[0105] The invention has been described in detail with particularreference to certain preferred embodiments thereof, but it will beunderstood that variations and modifications can be effected within thespirit and scope of the invention.

What is claimed is:
 1. A biaxially stretched, semicrystalline multilayerfilm base comprising at least two layers: a) a first layer of a firstPET-based polyester material comprising one or more polyester resins; b)adjacent on at least one side of the first layer a second layer of asecond PET-based polyester material comprising one or more polyesterresins, in which material the total level of repeat units derived from1,4-cyclohexane dimethanol is greater than the corresponding level inthe first layer, based on total glycol component in the material, andwherein the difference in the level of 1,4-cyclohexane dimethanolbetween the first and the second layer is less than 50 mol % based onthe total glycol component; wherein total level of repeat units derivedfrom 1,4-cyclohexane dimethanol in the first PET-based polyestermaterial is at least 3.5 mol % based on total glycol component in thematerial, except that when said second layer has a level of repeat unitsderived from 1,4-cyclohexane dimethanol that is between 3.5 and 25 mol%, based on total glycol component in the material, then the first layercan have less than 3.5 mol % 1,4-cyclohexane dimethanol, or none, basedon total glycol component; wherein at least the polyester material inthe second layer is semi-crystalline; wherein the total thickness ofsaid film base is 50 to 180 μm; and wherein the cutting index of saidmultilayer film base is less than 4.2
 2. The film base according toclaim 1 wherein the second layer comprises a second PET-based polyestermaterial in which the total level of repeat units derived from1,4-cyclohexane dimethanol is 3.5 to 25 mol % based on total glycolcomponent in the material, and the first layer comprises first PET-basedpolyester material in which the total level of repeat units derived from1,4-cyclohexane dimethanol is 0 to 25 mol % based on total glycolcomponent in the material.
 3. The film base of claim 1 in which the mainor first layer comprises first PET-based polyester material in which thelevel of repeat units derived from 1,4-cyclohexane dimethanol is atleast 10 mol % based on total glycol component in the material; and theouter or second layer of a second PET-based polyester material comprisesgreater than 60 mol % of repeat units derived from 1,4-cyclohexanedimethanol, based on total glycol component in the material, and whereinthe difference in the level of 1,4-cyclohexane dimethanol between themain and outer layer is less than 50 mol % based on total glycolcomponent in the material.
 4. The film base of claim 1 wherein themultilayer film based consists of only two layers, a first layer and asecond layer.
 5. The film base of claim 1 comprising at least threelayers, wherein the third layer, on the opposite side of the first layerfrom the second layer, comprises a third PET-based polyester materialcomprising one or more polyester resins, in which material the totallevel of repeat units derived from 1,4-cyclohexane dimethanol is greaterthan the level in the first layer, based on total glycol component inthe material; and wherein the difference in the level of 1,4-cyclohexanedimethanol between the first layer and any adjacent layer is less than50 mol % based on total glycol component in the material, and whereinthe composition of the second and third layers can be the same ordifferent.
 6. A biaxially stretched, semicrystalline multilayer filmbase comprising at least three layers: a) a core layer of a PET-basedpolyester material comprising one or more polyester resins; b) adjacentto both sides of the main layer, respectively, a first and a secondouter layer of a PET-based polyester material comprising one or morepolyester resins, in which material the total level of repeat unitsderived from 1,4-cyclohexane dimethanol is greater than the level in thecore layer, based on total glycol component in the material; wherein thetotal level of repeat units derived from 1,4-cyclohexane dimethanol inthe core layer is at least 3.5 mol % based on total glycol component inthe material except that when one or both of said first and second outerlayers has a level of repeat units derived from 1,4-cyclohexanedimethanol that is between 3.5 and 25 mol %, based on total glycolcomponent in the material, then the first layer can have less than 3.5mol %, or an absence of, 1,4-cyclohexane dimethanol; wherein thedifference in the level of 1,4-cyclohexane dimethanol between the mainlayer and any adjacent layer is less than 50 mol % based on total glycolcomponent.; wherein the total thickness of the film base is from 50 to180 μm; wherein at least the polyester material in at least one outerlayer or both outer layers is semi-crystalline, and wherein the cuttingindex of said multilayer film base is less than 4.2.
 7. The film base ofclaim 1 wherein the first layer is a CHDM-modified-PET polyester and thesecond layer is a high-CHDM-modified PET polyester comprising 100 mol %of 1,4-cyclohexane dimethanol based on its total glycol component. 8.The film base of claim 6 wherein the core layer is a CHDM-modified-PETpolyester and both outer layers consist of a high-CHDM-modified-PETpolyester comprising 100 mol % of 1,4-cyclohexane dimethanol based onits total glycol component.
 9. The film base of claim 1 wherein thefirst layer is the thickest layer in the film base.
 10. The film base ofclaim 6 wherein the main layer is the thickest layer in the film base.11. The film base of claim 1 wherein the thickness ratio of the firstlayer to the entire film base is 0.30 to 0.95.
 12. The film base ofclaim 1 wherein the ratio of the thickness of the second layer to thethickness of the entire film base is 0.05 to 0.40.
 13. The film base ofclaim 2 in which the level of repeat units derived from 1,4-cyclohexanedimethanol in the second layer is in the range of about 10 to 22 mol %,based on total glycol component in the material, and the cutting indexof said multilayer film base is less than 3.5.
 14. The film base ofclaim 6 in which the level of repeat units derived from 1,4-cyclohexanedimethanol in the outer layers is in the range of about 10 to 22 mol %,based on total glycol component in the material, and the cutting indexof said multilayer film base is less than 3.5.
 15. The film base ofclaim 1 wherein the PET-based polyester material in the first layer is amiscible blend of at least two PET-based polyesters, wherein bothpolyesters comprising repeat units derived from 1,4-cyclohexanedimethanol and the difference in the level of 1,4-cyclohexane dimethanolbetween the first and second layers (?) is less than 50 mol % based ontotal glycol component.
 16. The film base of claim 3 in which the levelof repeat units derived from 1,4-cyclohexane dimethanol in the firstlayer is in the range of about 20 to 25 mol %, based on total glycolcomponent in the material, and the cutting index of said multilayer filmbase is less than 3.5.
 17. The film base of claim 3 wherein thePET-based polyester material in the second layer comprises a miscibleblend comprising at least two polyesters, a first polyester being ahigh-CHDM-modified PET polyester in which the level of CHDM-comonomerunits is above about 95 mol %, and a second polyester comprising repeatunits derived from 1,4-cyclohexane dimethanol, wherein the total repeatunits derived from 1,4-cyclohexane dimethanol in the PET-based polyestermaterial is at a level of 60 to 100 mol %, based on total glycolcomponent in the polyester material.
 18. The film base of claim 1wherein the film base has a cutting index of less than 3.0.
 19. The filmbase of claim 1 wherein the film base has been manufactured by a processof melt extrusion, casting, biaxial stretching and heat-setting.
 20. Thefilm base of claim 1 wherein the film base has been heat treated attemperatures of from 50° C. up to Tg(H) for times ranging from 1 hr to1000 hrs where Tg(H) is the glass transition temperature of thepolyester with the highest glass transition temperature in themultilayer film.
 21. An imaging element comprising at least onelight-sensitive or heat-sensitive layer and the film base of claim 1.22. The imaging element of claim 21 wherein said first layer is nearerthan said second layer to said imaging layer and wherein the imaginglayer comprises a silver-halide emulsion.
 23. The imaging element ofclaim 21 wherein the light-sensitive imaging layer is sensitive to X-rayexposure.
 24. The imaging element of claim 21 wherein the element is aphotographic film or a photothermographic film.
 25. The imaging elementof claim 21 wherein the element is a 35-mm photographic film.
 26. Theimaging element of claim 21 further comprising a photographicallyacceptable subbing layer and backing layers on the film base.
 27. Theimaging element of claim 21 wherein the film base bears a magnetic oroptical recording layer.
 28. An imaging element comprising at least onelight-sensitive or heat-sensitive imaging layer over a supportcomprising a biaxially stretched, film base comprising at least twolayers: a) a first layer of a first PET-based polyester materialcomprising one or more polyester resins, b) adjacent on at least oneside of the first layer a second layer of a second PET-based polyestermaterial comprising one or more polyester resins, in which material thetotal level of repeat units derived from 1,4-cyclohexane dimethanol isgreater than the mol % in the first layer, based on total glycolcomponent in the material, and wherein there is less than a 50%difference in the mol percent of 1,4-cyclohexane dimethanol in the firstlayer and the second layer, wherein the mol % is based on the glycolcomponent; wherein total level of repeat units derived from1,4-cyclohexane dimethanol in the first PET-based polyester material isat least 3.5 mol % based on total glycol component in the material,except that when said second layer has a level of repeat units derivedfrom 1,4-cyclohexane dimethanol that is between 3.5 and 25 mol %, basedon total glycol component in the material, then the first layer can haveless than 3.5 mol % 1,4-cyclohexane dimethanol, or none, based on totalglycol component; wherein at least the polyester material in the secondlayer is semi-crystalline; wherein the total thickness of said film baseis 50 to 180 μm; and wherein the cutting index of said multilayer filmbase is less than 4.2.
 29. The imaging element of claim 28 wherein theTg of the polymers in the polyester material in at least the first andsecond layer, preferably all layers, of the multilayer film base is lessthan 90° C.